title: Molecular pharmacology and ligand docking studies reveal a single amino acid difference between mouse and human serotonin 5-HT2A receptors that impacts behavioral translation of novel 4-phenyl-2-dimethylaminotetralin ligands.
abstract: During translational studies to develop 4-phenyl-2-dimethylaminotetralin (PAT) compounds for neuropsychiatric disorders, the (2R,4S)-trans-(+)- and (2S,4R)-trans-(-)-enantiomers of the analog 6-hydroxy-7-chloro-PAT (6-OH-7-Cl-PAT) demonstrated unusual pharmacology at serotonin (5-HT) 5-HT2 G protein-coupled receptors (GPCRs). The enantiomers had similar affinities (Ki) at human (h) 5-HT2A receptors (≈ 70 nM). In an in vivo mouse model of 5-HT2A receptor activation [(±)-(2,5)-dimethoxy-4-iodoamphetamine (DOI)-elicited head twitch], however, (-)-6-OH-7-Cl-PAT was about 5-fold more potent than the (+)-enantiomer at attenuating the DOI-elicited response. It was discovered that (+)-6-OH-7-Cl-PAT (only) had ≈ 40-fold-lower affinity at mouse (m) compared with h5-HT2A receptors. Molecular modeling and computational ligand docking studies indicated that the 6-OH moiety of (+)- but not (-)-6-OH-7-Cl-PAT could form a hydrogen bond with serine residue 5.46 of the h5-HT2A receptor. The m5-HT2A as well as m5-HT2B, h5-HT2B, m5-HT2C, and h5-HT2C receptors have alanine at position 5.46, obviating this interaction; (+)-6-OH-7-Cl-PAT also showed ≈ 50-fold lower affinity than (-)-6-OH-7-Cl-PAT at m5-HT2C and h5-HT2C receptors. Mutagenesis studies confirmed that 5-HT2A S5.46 is critical for (+)- but not (-)-6-OH-7-Cl-PAT binding, as well as function. The (+)-6-OH-7-Cl-PAT enantiomer showed partial agonist effects at h5-HT2A wild-type (WT) and m5-HT2A A5.46S point-mutated receptors but did not activate m5-HT2A WT and h5-HT2A S5.46A point-mutated receptors, or h5-HT2B, h5-HT2C, and m5-HT2C receptors; (-)-6-OH-7-Cl-PAT did not activate any of the 5-HT2 receptors. Experiments also included the (2R,4S)-trans-(+)- and (2S,4R)-trans-(-)-enantiomers of 6-methoxy-7-chloro-PAT to validate hydrogen bonding interactions proposed for the corresponding 6-OH analogs. Results indicate that PAT ligand three-dimensional structure impacts target receptor binding and translational outcomes, supporting the hypothesis that GPCR ligand structure governs orthosteric binding pocket molecular determinants and resulting pharmacology.
authors.affiliation: Center for Drug Discovery (C.E.C., T.C.-S., Y.L., R.G.B.), Department of Pharmaceutical Sciences (C.E.C., T.C.-S., Y.L., R.G.B.), and Department of Chemistry and Chemical Biology (R.G.B.), Northeastern University, Boston, Massachusetts; and Department of Medicinal Chemistry (M.S.K., T.C.-S.) and Department of Psychiatry (D.M.), University of Florida, Gainesville, Florida.
authors.forename: Clinton E
authors.initials: CE
authors.lastname: Canal
authors.forename: Tania
authors.initials: T
authors.lastname: Cordova-Sintjago
authors.forename: Yue
authors.initials: Y
authors.lastname: Liu
authors.forename: Myong S
authors.initials: MS
authors.lastname: Kim
authors.forename: Drake
authors.initials: D
authors.lastname: Morgan
authors.forename: Raymond G
authors.initials: RG
authors.lastname: Booth
mesh_terms: D019943:Amino Acid Substitution; D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D001519:Behavior / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006868:Hydrolysis; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008958:Models, Molecular; D010716:Phosphatidylinositols / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D011869:Radioligand Assay; D044402:Receptor, Serotonin, 5-HT2A / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D058826:Serotonin 5-HT2 Receptor Agonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013045:Species Specificity; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013764:Tetrahydronaphthalenes / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000662:Amphetamines; D008024:Ligands; D010716:Phosphatidylinositols; D044402:Receptor, Serotonin, 5-HT2A; D058826:Serotonin 5-HT2 Receptor Agonists; D017366:Serotonin Receptor Agonists; D013764:Tetrahydronaphthalenes; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine